Device and method for transmitting and receiving discovery signal of base station in mobile communication system

ABSTRACT

A method by which a small base station (BS) transmits a discovery signal (DS) in a mobile communication system is provided. The method includes a macro BS to which a component carrier (CC) of a predetermined frequency band is allocated, and at least one small base station to which N number of CCs of a frequency band different from that of the CC allocated to the macro base station are allocated. The method comprises the steps of generating the DS corresponding to predetermined information and transmitting the generated DS through a discovery channel (DCH) configured as a transmission resource of the macro base station, wherein the predetermined information is one among information on at least one CC that the small base station uses, cell ID (CID) index information of the small base station, and a sleep base station index when the small base station is in a sleep mode.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a U.S. National Stage application under 35 U.S.C.§371 of an International application filed on Jul. 29, 2014 and assignedapplication number PCT/KR2014/006928, which claimed the benefit of aKorean patent application filed on Jul. 30, 2013 in the KoreanIntellectual Property Office and assigned Serial number 10-2013-0090180,the entire disclosure of which is hereby incorporated by reference.

TECHNICAL FIELD

The present disclosure relates to cell searching of a user equipment(UE) in a mobile communication system. More particularly, the presentdisclosure relates to a method and apparatus for a small base station(BS) to transmit a discovery signal, and for a UE to receive thediscovery signal, in a mobile communication system in which a macro BSand a small BS use component carriers of different frequency bands.

BACKGROUND

To address the shortage of frequency capacity, which is caused by thetendency of high capacity and high-speed communication in a cellularmobile communication system, a method of additionally installing a smallcell in an existing macro cell coverage has been discussed.

In this instance, to minimize the effect of interference to an existingsystem that mainly uses a macro cell, a separate frequency band schememay be used, in which a macro cell base station (BS) may use, forexample, a frequency of 2 GHz which is a relatively lower band, and asmall cell BS may use, for example, a frequency of 3.5 GHz which is arelatively higher band. In the separate frequency band scheme, high bandfrequency resources may include a larger number of dormant frequencyresources than low band frequency resources. Therefore, the separatefrequency band scheme is advantageous in that the system capacity may bedramatically improved by utilizing carrier aggregation (CA) technologythat uses multiple component carriers. For reference, the CA technology,which is introduced by 3rd generation partnership project (3GPP) Release10, is to increase a transmission speed by simultaneously utilizing aplurality of carriers.

Other aspects, advantages, and salient features of the disclosure willbecome apparent to those skilled in the art from the following detaileddescription, which, taken in conjunction with the annexed drawings,discloses various embodiments of the present disclosure.

SUMMARY

Aspects of the present disclosure are to address at least theabove-mentioned problems and/or disadvantages and to provide at leastthe advantages described below. Accordingly, an aspect of the presentdisclosure is to provide a method and apparatus for a user equipment(UE) to search for a small base station (BS) in a mobile communicationsystem.

Another aspect of the present disclosure is to provide a method andapparatus for a small BS to provide a UE with information associatedwith a component carrier (CC) that the small BS uses in a mobilecommunication system.

Another aspect of the present disclosure is to provide a method andapparatus for a small BS that operates in a dormant mode to inform a UEof the existence of the small BS itself in a mobile communicationsystem.

Another aspect of the present disclosure is to provide a method andapparatus for a macro BS to manage a dormant mode index for a small BSthat operates in a dormant mode in a mobile communication system.

Another aspect of the present disclosure is to provide a method andapparatus for a small BS to provide a UE with a cell ID (CID)configuration information index of the small BS in a mobilecommunication system.

In accordance with an aspect of the present disclosure, a method for asmall BS to transmit a discovery signal (DS) in a mobile communicationsystem that includes a macro BS to which a component carrier (CC) of apredetermined frequency band is assigned, and at least one small BS towhich N CCs are assigned, of which a frequency band is different fromthe CC assigned to the macro BS, is provided. The method includesgenerating a DS corresponding to predetermined information, andtransmitting the generated DS through a discovery channel (DCH) that isformed of transmission resources of the macro BS, wherein thepredetermined information is one of at least one CC information used bythe small BS, a CID configuration information index of the small BS, anda dormant BS index when the small BS is in a dormant mode.

In accordance with another aspect of the present disclosure, a methodfor a UE to receive a DS of a small BS in a mobile communication systemincluding a macro BS to which a CC of a predetermined frequency band isassigned, and at least one small BS to which N CCs are assigned, ofwhich a frequency band is different from the CC assigned to the macroBS, is provided. The method includes receiving a DCH that is formed oftransmission resources allocated to the macro BS, detecting a DSindicating predetermined information from the received DCH, andobtaining predetermined information from the detected DS, wherein thepredetermined information is one of at least one CC information used bythe small BS, CID index information of the small BS, and a dormant BSindex when the small BS is a dormant mode.

In accordance with another aspect of the present disclosure, anapparatus of a small BS for transmitting a DS in a mobile communicationsystem including a macro BS to which a CC of a predetermined frequencyband is assigned, and at least one small BS to which N CCs are assigned,of which a frequency band is different from the CC that is assigned tothe macro BS, is provided. The apparatus includes a controllerconfigured to transfer predetermined information to a DS generatingunit, the DS generating unit configured to generate a DS correspondingto the predetermined information, and a transceiving unit configured totransmit the generated DS through a DCH that is formed of transmissionresources of the macro BS, wherein the predetermined informationincludes one of at least one CC information used by the small BS, CIDindex information of the small BS, and a dormant BS index when the smallBS is in a dormant mode.

In accordance with another aspect of the present disclosure, anapparatus of a UE for receiving a DS a small BS, in a mobilecommunication system including a macro BS to which a CC of apredetermined frequency band is assigned, and at least one small BS towhich N CCs are assigned, of which a frequency band is different fromthe CC assigned to the macro BS, is provided. The apparatus includes atransceiving unit configured to receive a DCH that is formed oftransmission resources allocated to the macro BS, a DS detecting unitconfigured to detect a DS indicating predetermined information from thereceived DCH, and a controller configured to obtain the predeterminedinformation from the detected DS, wherein the predetermined informationincludes one of at least one CC information used by the small BS, CIDindex information of the small BS, and a dormant BS index when the smallBS is in a dormant mode.

In the present disclosure, the DS is generated using a singlepredetermined code or a predetermined number of orthogonal codes havingdifferent values.

In the present disclosure, when the predetermined information is the CCinformation and the DS is generated using a single predetermined code,the DCH includes N transmission areas that are mapped respectively to NCC values, and the DS is transmitted through a transmission area that ismapped to a CC information value corresponding to the DS.

In the present disclosure, when the predetermined information is the CCinformation and the DS is generated using a predetermined number oforthogonal codes, the orthogonal codes are formed of N orthogonal codesthat are mapped respectively to N CC information values, the DCHincludes a single transmission area for the transmission of the DS, andthe DS is transmitted through the single transmission area for thetransmission of the DS, irrespective of the CC information value.

In the present disclosure, when the predetermined information is a CIDconfiguration information index of the small BS, and the DS is generatedusing a single predetermined code, the DCH includes L transmission areasthat are mapped respectively to L CID configuration information indexvalues, and the DS is transmitted through a transmission area that ismapped to a CID configuration information index value corresponding tothe DS.

When the predetermined information is a CID configuration informationindex of the small BS, and the DS is generated using a predeterminednumber of orthogonal codes, the orthogonal codes are formed of Lorthogonal codes that are mapped respectively to L CID configurationinformation index values, the DCH includes a single transmission areafor the transmission of the DS, and the DS is transmitted through thesingle transmission area for the transmission of the DS, irrespective ofthe CID configuration information index value.

In the present disclosure, when the predetermined information is thedormant BS index and the DS is generated using a single predeterminedcode, the DCH includes K transmission areas that are mapped respectivelyto K dormant BS index values, and the DS is transmitted through atransmission area that is mapped to a dormant BS index valuecorresponding to the DS.

In the present disclosure, when the predetermined information is thedormant BS index and the DS is generated using a predetermined number oforthogonal codes, the orthogonal codes are formed of K orthogonal codesthat are mapped respectively to K dormant BS index values, the DCHincludes a single transmission area for the transmission of the DS, andthe DS is transmitted through the single transmission area, irrespectiveof the dormant BS index value.

In the present disclosure, when the small BS does not communicate with aUE during a predetermined period of time, the small BS enters a dormantmode, transmits, to the macro BS, at least one of a dormant modeindicator indicating that the small BS in a dormant mode and CCinformation used by the small BS, and receives the dormant BS index fromthe macro BS.

In the present disclosure, when an active mode entry message is receivedfrom the macro BS, the small BS cancels the dormant mode and enters theactive mode.

In the present disclosure, the DCH area is determined based on DCHlocation information that is transferred in advance from the macro BS,and the DCH location information may be fixed to a predetermined areaamong transmission resources of the macro BS, or may be determined basedon a CID of the macro BS.

In the present disclosure, in the case where the predeterminedinformation is the CC information when the small BS selects a CC to beused, a CC having the smallest traffic, or a CC that is not used by anadjacent small BS, may be selected out of available CCs.

In the present disclosure, a downlink resource or an uplink resource ofthe macro BS may be used as a transmission resource of the macro BS.

In the present disclosure, when the predetermined information is the CCinformation and the DS is generated using a single predetermined code, aUE obtains the CC information from the DS using CC-based S-DS locationinformation, which is provided in advance from a macro BS.

In the present disclosure, when the predetermined information is the CCinformation and the DS is generated using a predetermined number oforthogonal codes, a UE obtains the CC information using the mappingrelationship between CCs and orthogonal codes, and S-DS locationinformation, which are provided in advance from a macro BS.

In the present disclosure, when the predetermined information is a CIDconfiguration information index of the small BS, and the DS is generatedusing a single predetermined code, a UE obtains the CID configurationinformation index from the DS using S-DS location information for eachCID configuration information index, which is provided in advance from amacro BS.

In the present disclosure, when the predetermined information is a CIDconfiguration information index of the small BS, and the DS is generatedusing a predetermined number of orthogonal codes, a UE obtains the CIDconfiguration information index using the mapping relationship betweenCID configuration information indices and orthogonal codes and the S-DSlocation information, which are provided in advance from a macro BS.

In the present disclosure, the number of dormant BS indices may be setto be smaller than the number of small BSs. In this instance, when thenumber of dormant BS indices is smaller than the number of dormant modesmall BSs, a single dormant BS index may be allocated to a plurality ofsmall BSs. In this instance, a single dormant BS index may be allocatedto a plurality of small BSs, which are geographically distant from oneanother.

In accordance with another aspect of the present disclosure, a methodfor a macro BS to control a small BS in a mobile communication systemthat includes the macro BS to which a CC of a predetermined frequencyband is assigned, and at least one small BS to which N CCs are assigned,of which a frequency band is different from the CC that is assigned tothe macro BS, is provided. The method includes receiving a dormant modeentry message from a dormant mode small BS, transmitting a predetermineddormant BS index to the small BS, receiving the dormant BS index from aUE that receives, from the dormant mode small BS, a discovery signalindicating the dormant BS index, and transmitting an active mode entrymessage to the dormant mode small BS.

Also, the method further includes receiving, from the small BS, thedormant BS index and CC information used by the small BS andtransmitting the received CC information to the UE.

In accordance with another aspect of the present disclosure, a macro BSthat controls a small BS in a mobile communication system including themacro BS to which a CC of a predetermined frequency band is assigned,and at least one small BS to which N CCs are assigned, of which afrequency band is different from the CC assigned to the macro BS, isprovided. The macro BS includes a transceiving unit that receives adormant mode entry message from a dormant mode small BS, a controllerthat controls a message generating unit to generate a predetermineddormant BS index, and a message generating unit that generates thedormant BS index under the control of the controller and transmits thesame to the small BS through the transceiving unit, wherein thecontroller controls the message generating unit to transmit an activemode entry message to the dormant mode small BS when receiving thedormant BS index through the transceiving unit from a UE that receives adiscovery signal indicating the dormant BS index from the dormant modesmall BS.

The controller receives the dormant BS index and CC information used bythe small BS through transceiving unit from the small BS, and transmitsthe received CC information to the UE through the transceiving unit.

Effects that may be achieved through the construction of the presentdisclosure will be briefly described as follows.

In the present disclosure, when a macro BS and a small BS use CCs ofdifferent frequency bands, the small BS transmits a discovery signalusing a transmission resource of an f0 band that was assigned to themacro BS, so as to inform a UE of the existence of the small BS.

The UE may recognize that the small BS exists by executing a searchthrough the f0 band, which is a frequency band of a CC used by the macroBS, instead of executing a search through N frequency bands f1 to fNthat were assigned to the small BS. Therefore, the UE may notcontinuously execute a search through a frequency band of the small BSand, thus, the amount of power consumed in the UE may be reduced.

Also, the present disclosure provides frequency information of a CC usedby a small BS through a discovery signal of the small BS and, thus, a UEmay reduce the cell association time for a cell association with thesmall cell.

Also, in the present disclosure, when a small BS operates in a dormantmode, the small BS reports that the small BS operates in the dormantmode through a discovery signal. Accordingly, when a new UE enters thesmall BS that operates in the dormant mode, the UE may promptlyrecognize that the small BS that operates in the dormant mode exists ina nearby location, and subsequently, may enable the small BS of thedormant mode into an active mode, thereby reducing a cell associationdelay between the UE and the small BS.

Also, in the present disclosure, a small BS provides a CID configurationinformation index that may configure a CID of the small BS to a UEthrough a discovery signal, thereby increasing the number of CIDs in awhole system.

Other aspects, advantages, and salient features of the disclosure willbecome apparent to those skilled in the art from the following detaileddescription, which, taken in conjunction with the annexed drawings,discloses various embodiments of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certainembodiments of the present disclosure will be more apparent from thefollowing description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a diagram illustrating a separate frequency band mobilecommunication system according to an embodiment of the presentdisclosure;

FIG. 2 is a diagram illustrating an example of cell searching based on alocation of a user equipment (UE) in a separate frequency band systemaccording to an embodiment of the present disclosure;

FIG. 3 is a diagram illustrating resource allocation of a macro basestation (BS) and a small BS in a separate frequency band systemaccording to an embodiment of the present disclosure;

FIG. 4 is a diagram illustrating an example in which a small BS selectsa component carrier (CC) according to a first embodiment of the presentdisclosure;

FIG. 5 is a diagram illustrating an example of generating an discoverysignal (S-DS) using a single code according to a first embodiment of thepresent disclosure;

FIG. 6 is a diagram illustrating an example of generating an S-DS usingorthogonal codes having different values according to a first embodimentof the present disclosure;

FIG. 7 is a diagram illustrating a process in which a UE receives anS-DS transmitted by a small BS according to a first embodiment of thepresent disclosure;

FIG. 8 is a diagram illustrating an operation in which a small BSgenerates and transmits an S-DS according to a first embodiment of thepresent disclosure;

FIG. 9 is a diagram illustrating an operation in which a UE receives anS-DS according to a first embodiment of the present disclosure;

FIG. 10 is a diagram illustrating a process in which a small BS isbilaterally converted between a dormant mode and an active modeaccording to a second embodiment of the present disclosure;

FIG. 11 is a diagram illustrating a structure of an small BS-discoverychannel (S-DCH) according to a second embodiment of the presentdisclosure;

FIG. 12 is a diagram illustrating a configuration of another small BSaccording to various embodiments of the present disclosure;

FIG. 13 is a diagram illustrating a UE according to various embodimentsof the present disclosure;

FIG. 14 is a diagram illustrating a method of a macro BS according to asecond embodiment of the present disclosure; and

FIG. 15 is a diagram illustrating a macro BS according to a secondembodiment of the present disclosure.

Throughout the drawings, it should be noted that like reference numbersare used to depict the same or similar elements, features, andstructures.

DETAILED DESCRIPTION

The following description with reference to the accompanying drawings isprovided to assist in a comprehensive understanding of variousembodiments of the present disclosure as defined by the claims and theirequivalents. It includes various specific details to assist in thatunderstanding but these are to be regarded as merely exemplary.Accordingly, those of ordinary skill in the art will recognize thatvarious changes and modifications of the various embodiments describedherein can be made without departing from the scope and spirit of thepresent disclosure. In addition, descriptions of well-known functionsand constructions may be omitted for clarity and conciseness.

The terms and words used in the following description and claims are notlimited to the bibliographical meanings, but, are merely used by theinventor to enable a clear and consistent understanding of the presentdisclosure. Accordingly, it should be apparent to those skilled in theart that the following description of various embodiments of the presentdisclosure is provided for illustration purpose only and not for thepurpose of limiting the present disclosure as defined by the appendedclaims and their equivalents.

It is to be understood that the singular forms “a,” “an,” and “the”include plural referents unless the context clearly dictates otherwise.Thus, for example, reference to “a component surface” includes referenceto one or more of such surfaces.

In addition, terms, such as first, second, or the like, may be usedherein when describing various components of the present disclosure.Each of these terminologies is not used to define a correspondingcomponent but used merely to distinguish the corresponding componentfrom other component(s). For example, a first component element may bereferred to as a second component element, and similarly, the secondcomponent element may be referred to as the first component elementwithout departing the scope and sprit of the disclosure. The term, suchas “and/or”, includes a combination of a plurality of related mentioneditems or one of the plurality of related mentioned items.

As used herein, terms are used merely for describing specificembodiments are not intended to limit the present disclosure. Thesingular terms cover plural components unless the singular terms haveapparently different meaning contextually. In this application, terms,such as “comprise” or “have,” shall be understood that they are usedmerely for designating that corresponding features, numbers, steps,actions, components, parts or the combinations thereof may exist, butnot excluding in advance the possibility of existence or addition of thefeatures, the numbers, the steps, the actions, the components, the partsor the combinations thereof.

Unless defined otherwise, all the terms including technical orscientific terms used herein have the same meaning as those understoodgenerally by a person having an ordinary skill in the art. The termshaving the same meaning as those defined in generally used dictionariesshall be construed to have the meaning conforming to the contextualmeaning of the related technologies, and shall not be construed as idealor excessively formal meaning unless the terms are apparently defined inthis application.

Hereinafter, detailed descriptions of the present disclosure will bedescribed with reference to the accompanying drawings, which illustratespecific embodiments by which the present disclosure may be carried out.

Terms and abbreviations used in the present specification will bedescribed first.

“Macro cell base station (BS)”, “macro BS”, and “m-BS” may beinterchangeably used.

“Small cell BS” is a BS having a small coverage, which is under themanagement of a macro BS or is independent from the macro BS, and “smallcell BS”, “small BS”, and “s-BS” are interchangeably used. That is, thesmall cell BS may be dependent upon the macro cell BS or may have aparallel relationship with the macro cell BS.

“Mobile terminal”, “terminal”, and “user equipment (UE)” areinterchangeably used.

“Component carrier” indicates each carrier used in the carrieraggregation (CA) technology in a mobile communication system, which isabbreviated to “CC”.

“Discovery Signal” is a signal used when a BS informs ambient entitiesof the existence of the BS itself, which is abbreviated to “DS”. In thepresent disclosure, a discovery signal of a small BS is mainlydescribed, and thus, the DS will be referred to as an S-DS which is adiscovery signal of a small BS. Also, the S-DS may be abbreviated to“DS”, and here, the DS indicates an S-DS, unless otherwise noted.

“Cell searching” indicates that a UE searches for a macro BS/small BSlocated around the UE to execute communication, which includesmonitoring a frequency band of a corresponding BS.

Before giving a detailed description of the present disclosure, it ishelpful to give a brief overview of the present disclosure.

According to the present disclosure, in a wireless communication systemor a mobile communication system that includes a first BS that uses acomponent carrier of an f0 band and second BSs to which componentcarriers of N frequency bands are assigned, the N frequency bands beingdifferent from f0, the second BS generates a discovery signal forreporting the existence of the second BS to UEs within a coverage of thesecond BS, and transmits the discovery signal through a transmissionresource of the f0 band. For example, the first BS may be a macro BS,and the second BS may be a small BS. Hereinafter, descriptions will beprovided from the perspective of a macro BS and a small BS.

The discovery signal may indicate information used for communicationbetween a small BS and a UE. A first embodiment of the presentdisclosure will describe that a discovery signal indicates CCinformation used by a small BS. A second embodiment of the presentdisclosure will describe that a small BS operates in a dormant mode whena UE does not exist within a coverage of the small BS during apredetermined period of time, and a discovery signal indicates dormantmode index information to report that the small BS operates in thedormant mode in case a new UE enters the coverage when the small BSoperates in the dormant mode. Also, a third embodiment of the presentdisclosure will describe that a discovery signal indicates a cellidentification (CID) configuration information index that may configurea CID of a small BS.

The description in one embodiment may be applied to another embodiment,except for a case of apparent contradiction. Therefore, the embodimentsof the present disclosure are distinguished for ease of description, andthe embodiments may not always be implemented by being distinguished,but may be implemented in parallel.

Hereinafter, the embodiments of the present disclosure will be describedin detail.

FIG. 1 is a diagram illustrating a separate frequency band mobilecommunication system according to an embodiment of the presentdisclosure.

Referring to FIG. 1, a plurality of small BSs 103, 105, and 107 areinstalled in a macro BS 101. Referring to FIG. 1, three small BSs areillustrated. It is illustrated that a plurality of UEs 111, 113, 115,117, 119, 121, and 127 are located in an area of the macro BS 101. Also,some of the UEs 111, 113, 115, 117, 119, 121, and 127 are located inareas of the small BSs 103, 105, and 107. For example, some UEs 117 and119 are located in the area of the small BS 107, and other UEs 121 and127 are located in the area of the small BS 105. Some UEs 111, 113, and115 are located in the area of the macro BS 101 but are not located inany small BS's area.

It is assumed that the macro BS 101 uses a frequency of 2 GHz 131, whichis a relatively low band, and the small BSs 103, 105, and 107 usesfrequencies f1, f2, . . . , f5 133 based on 3.5 GHz, which arerelatively high band.

In the separate frequency band system as shown in FIG. 1, a UE may needto recognize the existence of the macro BS 101 or the small BSs 103,105, and 107. To this end, the UE executes a search through both the 2GHz band, which is a frequency of the macro BS 101, and the 3.5 GHzband, which is a frequency of the small BSs 103, 105, and 107, so as toreceive a reference signal that is transmitted by corresponding BSs 101,103, 105, and 107.

The macro BS is designed to have a broad coverage area and transmits asignal at a relatively high transmission power, and thus, an area wherea UE is located may be generally included in the coverage of the macroBS. Therefore, generally, a UE executes a search through the 2 GHz band,which is the frequency band the macro BS, so as to receive, from themacro BS, information used for operations of the UE.

Conversely, the small BS is designed to have a relatively narrowcoverage area and thus, transmits a signal at a relatively lowtransmission power. When a UE is located far from the small BS andexists outside the coverage of the small BS, the corresponding UE maynot receive a signal transmitted from the small BS. An example isdepicted in FIG. 2.

FIG. 2 is a diagram illustrating an example of cell searching based on alocation of a UE in a separate frequency band system according to anembodiment of the present disclosure.

Referring to FIG. 2 is a separate frequency band system as shown in FIG.1, and illustrates that a single small BS 107 and two UEs, that is, UE1117 and UE2 113, are included in the single macro BS 101, for ease ofdescription. As described in FIG. 1, the macro BS 101 uses CC (f0) ofthe 2 GHz band, and CCs (f1˜f5) of the 3.5 GHz band are assigned to thesmall BS 107. However, it is assumed that the small BS 107 uses f2 andf3 out of the CCs (f1˜f5) of the 3.5 GHz band. The UE1 117 receivessignals of f0 of the 2 GHz band and f2 and f3 of the 3.5 GHz band asshown in the diagram (a), since the UE1 117 is located in both thecoverage of the macro BS 101 and the coverage of the small BS 107.Conversely, the UE2 113 is located in the coverage of the macro BS 101but is out of the coverage of the small BS 107, and thus, the UE2 113receives the signal of f0 of the 2 GHz band but fails to receive thesignals of f2 and f3 of the 3.5 GHz band as shown in the diagram (b).

In the above described example, searching through the 3.5 GHz band,which is the frequency of the small BS 107, may cause the UE2 113 toconsume unnecessary power. Particularly, when the small BS uses the CAtechnology and multiple component carriers (CCs) are used, the UE mayneed to independently execute a search through each of the multiple CCs,generally. Therefore, in this instance, the amount of power consumed ina UE may increase in proportion to the number of CCs.

When a UE that is incapable of recognizing which small BS exists inadvance, the UE should receive reference signals transmitted from eachof a macro BS and small BSs through a periodic search through the f0band used by the macro BS and the f1, . . . , fN used by the small BSs.Accordingly, when comparing a single frequency band system, in which amacro BS transmits a reference signal and a UE executes a search throughonly the F0 band, and the separate frequency band system, in which theUE executes a search through both the f0 band used by the macro BS andthe f1, . . . , fN bands used by the small BSs, the amount of powerconsumed in the UE in the separate frequency band system may increase inproportion to the number (N) of separate frequency bands.

In the present disclosure, a small BS sets a predetermined area of atransmission resource of a frequency band (f0) of a macro BS, as adiscovery channel of the small BS (small BS-discovery channel (S-DCH)).Also, the small BS generates a discovery signal of a small BS (S-BSdiscovery signal (S-DS)) defined in the present disclosure, andtransmits the same through the S-DCH, and a UE detects the S-DS from theS-DCH of the f0 band so as to reduce the amount of power consumed in theUE.

The UE may obtain information used for communication with the small BS,using the detected S-DS. The information used for the communication mayinclude, for example, CC information that a corresponding small BScurrently uses, dormant index information for reporting that a small BSoperates in a dormant mode when the small BS operates in the dormantmode, or a cell ID (CID) configuration information index for configuringa CID of the corresponding small BS.

The first embodiment will describe that a small BS indicates CCinformation through an S-DS. The second embodiment will describe that asmall BS reports a dormant BS index through an S-DS when the small BS isa dormant BS. The third embodiment will describe that a small BS reportsa CID configuration information index of the small BS through an S-DS.

Hereinafter, frequency allocation to enable a small BS to transmit adiscovery signal will be described with reference to FIG. 3.

FIG. 3 is a diagram illustrating resource allocation with respect to amacro BS and a small BS for the transmission of a discovery signal, in aseparate frequency band system according to an embodiment of the presentdisclosure.

In the present disclosure, the small BS generates a discovery signal(S-DS) and transmits the same using a transmission resource of thefrequency band (f0) of the macro BS, so as to inform neighboring UEs ofthe existence of the small BS.

In the present disclosure, a predetermined resource area in the f0 bandthrough which a discovery signal is transmitted is defined as a“discovery channel of a small BS (S-DCH)”. In the present disclosure,some or all of a downlink (DL) resource or an uplink (UL) resource inthe f0 band, which were allocated to the macro BS, may be used for theS-DCH.

Referring to FIG. 3, downward arrows 301, 305, 307, and 309 indicatedownlink transmission in which the macro BS 101 or the small BS 107transmits a signal to a UE, and upward arrows 303 and 311 indicate thatthe macro BS 101 or the small BS 107 receives an uplink transmissionsignal of a UE. Also, solid line boxes 321, 325, and 329 indicate that aDL resource is used. Broken line boxes 323, 327, and 331 indicate that aUL resource is used.

That is, in the diagram 351, the solid line arrow 301 and the solid linebox 321 indicate that the macro BS 101 executes a downlink transmissionof control/user data using a downlink resource of the f0 band. Thebroken line arrow 303 and the broken line box 323 indicate that themacro BS 101 receives control/user data using an uplink resource in thef0 band.

In the diagram 353, the solid line arrow 305 and the solid line box 325indicate that the small BS 107 executes a downlink transmission using adownlink resource of the f0 band, which is a frequency that wasoriginally allocated to the macro BS 101. A small box 341 inside thesolid line box 325 is a discovery channel (S-DCH) of the small BS 107,according to the present disclosure, and indicates that some of thedownlink resources of the f0 band is used.

The broken line arrow 307 and the broken line box 327 indicate adownlink transmission using an uplink resource of the f0 band, which wasoriginally allocated to the macro BS 101. A small box 343 inside thebroken line box 327 is an S-DCH of the small BS 107, and indicates thatsome of the uplink resource of the f0 band is used.

In the diagram 355, the solid line arrow 309 and the solid line box 329indicate that the small BS 107 executes a downlink transmission ofcontrol/user data using a downlink resource of the fk band, which wasoriginally allocated to the small BS 107. The broken line arrow 311 andthe broken line box 331 indicate that the small BS 107 receivescontrol/user data using an uplink resource in the fk band.

In the above described example, the diagram 351 uses f0, which is afrequency band that was originally allocated to the macro BS 101, andthe diagram 355 uses fk, which is a frequency band that was originallyallocated to the macro BS 101, which are identical to a general resourceallocation scheme. Conversely, the diagram 353 shows that a downlinkresource and an uplink resource of the f0 band, which were originallyallocated to the macro BS 101, are allocated to a discovery channel ofthe small BS 107. Accordingly, the diagram 353 shows that a transmissionresource of a macro BS is allocated to a discovery channel of a small BSaccording to a scheme proposed in the present disclosure.

As described in the descriptions with reference to FIG. 3, an S-DCHwhich is a transmission resource for the transmission of an S-DS, isallocated and thus, the small BSs include an S-DS in the S-DCH fortransmission. In this instance, a small BS may execute transmission byincluding, in an S-DS, information associated with operations andmanagement of the corresponding small BS.

First Embodiment

Hereinafter, the first embodiment, in which CC information used by asmall BS is indicated by an S-DS, will be described.

When a small BS desires to generate an S-DS, the small BS determines aCC to be used, first. As described in FIGS. 1 and 2, it is assumed thata macro BS uses a single CC and N CCs are additionally allocated tosmall BSs in a separate frequency band system. In this instance, a smallBS may use only M CCs out of the N available CCs (M=<N), so as to reduceinterference to an adjacent cell and unnecessary power consumption.

Generally, an M value becomes large as the number of UEs that desire toreceive a service from a corresponding small BS increases. As the smallBS uses a larger value, the small BS is capable of using a broaderbandwidth and thus, the capacity of data that may be transmitted by thesmall BS may increase. Therefore, small BSs use different M values basedon their environments, and may select a combination of M CCs out of thegiven N CCs to be different from one another. Each small BS may transferall or some of the information that is associated with M CCs used by acorresponding small BSs to neighboring UEs through an S-DS. Hereinafter,an example of a scheme of selecting and transferring one of the M CCinformation will be described.

FIG. 4 is a diagram illustrating an example of selecting one of M CCsthat a small BS uses, so as to transfer CC information through an S-DS,according to a first embodiment of the present disclosure.

Referring to FIG. 4, it is assumed that, M=2, a small BS1 401 uses f1and f4, a small BS2 402 uses f3 and f4, and the small BS1 401 and thesmall BS2 402 are close to one another. Also, it is assumed that two UEsare allocated in f1, and 10 UEs are allocated in f4, in the small BS1401.

In the present disclosure, when a small BS selects a CC, two schemes areconsidered. A first scheme is to select a CC having the smallest trafficby taking into consideration traffic of a corresponding frequency. Asecond scheme is to select a CC that is not used by an adjacent smallBS. In FIG. 4, when the small BS1 401 selects a CC according to thefirst scheme, the small BS1 401 selects f1 which is a CC having asmallest number of allocated UEs, out of f1 and f4. When the small BS2402 selects a CC according to the second scheme, the small BS2 402 mayselect f3 which is not used by the small BS1 401 that is an adjacent BS,out of f3 and f4. However, depending on cases, a predetermined CC whichis set as a default may be used.

Hereinafter, a scheme of generating an S-DS corresponding to a CCselected by a small BS in FIG. 4 will be described with reference toFIGS. 5 and 6. Two schemes may be used to generate an S-DS. A firstscheme is a case when all of the codes included in an S-DS have anidentical value, irrespective of a type of CC. A second scheme is a casewhen the codes included in an S-DS have different values based on a typeof CC, that is, orthogonal codes are used.

FIG. 5 is a diagram illustrating an example of generating an S-DS usinga single code according to the first embodiment of the presentdisclosure.

Referring to FIG. 5, an S-DCH 500 includes resource areas 501, 502, 503,. . . , 50N) through which an S-DS may be transmitted for each CC, so asto indicate a CC used by a corresponding small BS out of f1˜fN. That is,the areas 501, 502, 503, . . . , 50N may be areas through which S-DSscorresponding to CC frequencies f1, f2, f3, . . . , fN are transmitted.When a predetermined code (here, expressed as k) is inserted into eacharea, this may indicate that a CC that corresponds to the correspondingarea is used by a small BS.

That is, in FIG. 5, a location where an S-DS formed of a singlepredetermined code (k) is transmitted may indicate a corresponding CC,irrespective of a CC frequency. For example, the area 501 is mapped tof1, the area 502 is mapped to f2, . . . , and the area 50N is mapped tofN. Although FIG. 5 illustrates that the areas 501, 502, 503, . . . ,and 50N are consecutive, the areas may not need to be consecutive. Aslong as a predetermined area indicates a predetermined CC, it does notmatter if the areas are separated.

Both a UE and a small BS may need to know “CC-based S-DS locationinformation (or S-DCH location information)”. To this end, a macro BSprovides “CC-based S-DS location information” to UEs in a correspondingcoverage by including the same in a broadcasting message or a generalcontrol message. Also, mapping information may be transferred to a smallBS through a backhaul network.

For example, in the case of an LTE system, when an S-DS is transmittedon a physical downlink shared channel (PDSCH) defined in the long-termevolution (LTE) system, a location of an S-DS for each CC is fixed to apredetermined area on the PDSCH, and information thereof may be providedto UEs.

For example, when N=4, a location of an S-DS corresponding to f1 isfixed to (1, 1) of a (frequency, time) pair of a PDSCH, a location of anS-DS corresponding to f2 is fixed to (1, 2) on the PDSCH, a location ofan S-DS corresponding to f3 is fixed to (1, 3), . . . , and a locationof an S-DS corresponding to fN is fixed to (1, N), and the locationinformation of an S-DS for each CC may be transferred to a UE. When anarea of a transmission resource through which the S-DS is transmitted,is determined, a collision with an existing system should be prevented.For example, a general control signal and a reference signal (RS) aretransmitted on a PDSCH. In this instance, to avoid a collision with alocation where the control signal and the reference signal aretransmitted, the location of an S-DS may need to be set to a resourcearea where the control signal and the reference signal are nottransmitted.

The location of the S-DCH may be determined based on a functionassociated with a cell identification (CID) of a macro BS. For example,small BSs that belong to a macro BS of which a CID is “1” may set thelocation of an S-DCH to an area of number 1 that includes N resources ona PDSCH, and may set the N resources to sequentially correspond tof1˜fN. When an area of an S-DCH, where an S-DS is transmitted, isdetermined using a CID as a function, small BSs located in coverages ofmacro BSs having different CIDs may transmit an S-DS in differentresource areas. In this instance, a UE may obtain a CID of a macro BSthrough a synchronization signal on an existing PDSCH, and thus, aseparate transmission resource for reporting the location information ofthe S-DS to a UE may not be needed, which is advantageous. However, asmall BS may not always need to belong to a predetermined macro BS. Forexample, small BSs located in an overlapping area of the coverages oftwo macro BSs may transmit an S-DS through an S-DCH area correspondingto a CID of each of the two macro BSs.

Referring again to FIG. 5, FIG. 5 illustrates a case in which two smallBSs select f1 and f4, respectively, and transmit an S-DS using a singlepredetermined code (k), or a case in which a single small BS select twoCCs, f1 and f4, and transmits an S-DS using a single predetermined code(k). By assuming the latter case, a small BS selects f1 and f3,accordingly, the small BS transmits a single predetermined code (k) inlocations 501 and 503 on the S-DCH 500, which correspond to f1 and f3.UEs measure the strength of a reception signal in each of thetransmission areas 501 to 50N on an S-DCH, based on S-DCH locationinformation, and when an area of which a measured reception signalstrength is greater than or equal to a predetermined threshold value isdetected, the UEs may recognize that a small BS that uses a CCcorresponding to the area exists.

FIG. 6 is a diagram illustrating an example of generating an S-DS usingorthogonal codes having different values according to a first embodimentof the present disclosure.

Referring to FIG. 6, CCs used by a small BS may be distinguished usingorthogonal codes having different values. For example, when CCs that areavailable for the small BS are f1, f2, f3, and f4, the CCs aredistinguished by respectively mapping orthogonal codes a1, a2, a3, and 4having different values to f1, f2, f3, and f4. Also, each small BSgenerates an S-DS using orthogonal codes corresponding to some or all ofthe CCs that are available for a corresponding small BS, and transmitsthe same by inserting the same into a predetermined S-DCH 600 in the f0band resources.

For example, in the case of the LTE system, each small BS inserts anS-DS generated by itself into a predetermined location of a PDSCH, andtransmits the same. For example, when a small BS1 uses f1 and a smallBS2 uses f3, the small BS1 generates an orthogonal code a1 as an S-DS,inserts the same into an S-DCH on the PDSCH, and transmits the same. Thesmall BS 2 generates an orthogonal code a3 as an S-DS, inserts the sameinto a location of an S-DCH on the PDSCH, and transmits the same. Inthis instance, the location of the S-DCH where the small BS1 inserts anSODS and the location of the S-DCH where the small BS2 inserts an S-DSare identical.

A UE may need to know a mapping relationship between CC (f1, f2, f3, andf4) and an orthogonal code value (a1, a2, a3, and a4), and an S-DCHlocation where an S-DS is inserted. The mapping relationship between CCsand orthogonal codes and the S-DS location information (that is, S-DCHlocation information) may be provided to UEs through a broadcastingmessage or a control message transmitted by a macro BS, and may beprovided to a small BS through a backhaul network, as described in FIG.5. The mapping relationship between CCs and orthogonal codes may befixed or may be changed based on a function associated with a CID of themacro BS. In the same manner, the S-DCH location information may befixed to a predetermined location on a PDSCH, or may be changed for eachmacro BS based on a function associated with a CID of a macro BS.

As described above, the UE is aware of the S-DCH location informationand the mapping relationship between CCs and orthogonal codes and thus,the UE may detect a1 and a3 using a correlation measurement valuebetween a signal received in the S-DCH area on the PDSCH based on thelocation information and the orthogonal codes a1, a2, a3, and a4. Thatis, the UE may measure a correlation with the signal received in theS-DCH area on the PDSCH using the candidate orthogonal codes a1, a2, a3,and a4, which are known to the UE, may regard an orthogonal code ofwhich a measured correlation value is greater than or equal to apredetermined threshold value as an S-DS that is transmitted by thesmall BS, and may recognize a CC used by the small BS.

In the above described example, S-DS 1 (that is, code value a1) that istransmitted by the small BS1 and S-DS 2 (that is, code value a3) that istransmitted by the small BS2 are included in the S-DCH area on thePDSCH. Accordingly, when a UE uses a1 out of the candidate orthogonalcodes, S-DS 1 transmitted by the small BS 1 may be detected. When the UEuses a3 out of the candidate orthogonal codes, S-DS 2 transmitted by thesmall BS 2 may be detected. When the UE uses a2 or a4, a signal may notbe detected. In this instance, the UE selects a signal having a strongersignal strength out of two detected signals, and executes procedures toperform communication with a small BS in a CC band corresponding to acode value of the selected S-DS.

When comparing the scheme of FIG. 5 and the scheme of FIG. 6, thefollowing difference may be found. In FIG. 5, the CCs used by small BSsare distinguished based on a location where an S-DS is transmitted.Therefore, each small BS uses an identical code value when generating anS-DS. Conversely, in FIG. 6, S-DSs are generated using differentorthogonal code values whereby the CCs used by small BSs aredistinguished. Therefore, when a small BS generates an S-DS, the smallBS uses an orthogonal code value that is different based on a CC used bythe small BS. However, S-DSs having different values for each CC may betransmitted in an identical location.

Hereinafter, a process in which UEs receive an S-DS transmitted by asmall BS will be described.

FIG. 7 is a diagram illustrating a process in which a UE receives anS-DS transmitted by a small BS according to a first embodiment of thepresent disclosure.

Referring to FIG. 7, it is assumed that the small BS1 401 and small BS2402 select f1 703 and f3 704, respectively, as described in FIG. 4, anda UE1 701 is adjacent to the small BS1 401, and a UE2 702 is adjacent tothe small BS2 402. Also, in FIG. 7, the small BSs may generate S-DSsaccording to the scheme described in FIG. 5 or FIG. 6. In FIG. 7,however, it is assumed that an S-DS is generated using a single code (k)as described in FIG. 5, for ease of description.

The small BS1 401 generates an S-DS using a predetermined code (k),inserts the same into an area 711 corresponding to f1, in an S-DCH area709 on a PDSCH 710, and transmits the same. The small BS2 402 generatesan S-DS using a predetermined code (k), inserts the same into an area713 corresponding to f3, in the S-DCH area 709 on the PDSCH 710, andtransmits the same.

To detect an S-DS transmitted from the small BSs 401 and 402 and toobtain CC information, each UE 701 and 702 measures a strength of areception signal in each of N (FIG. 7 assumes that N is 5) S-DStransmission areas 711, 712, 713, 714, and 715 using locationinformation of the S-DCH 709, which may be previously known to the UEs.

In the S-DCH 709, an S-DS (k) transmitted by the small BS1 401 isincluded in the area 1 711, and an S-DS (k) transmitted by the small BS2402 is included in the area 3 713. Among the strength of a receptionsignal measured by the UE1 701 in each of the 5 S-DS transmission areas711, 712, 713, 714, and 715, a strength 705 measured in the area 1 711that includes the S-DS (k) transmitted by the small BS1 401 is thestrongest. A strength 706 of a reception signal measured in the area 3713 that includes the S-DS (k) transmitted by the small BS2 402 isweaker than the strength 705 of a signal measured in the area 1 711.When the signal strength in the area 3 713 is less than a predeterminedthreshold value and the signal strength in the area 1 711 is greaterthan or equal to a predetermined threshold value, the UE1 701 maydisregard the signal detected from the area 3 713 and may recognize thata small BS that uses f1 exists in a region near the UE1 701 based on thesignal detected from the area 1 711.

However, the UE1 701 only recognizes that a small BS that uses f1currently exists, but does not know that the corresponding small BS isthe small BS1 701. Therefore, the UE1 701 recognizes that a small BSthat uses f1 exists by executing a search through the current f0 band.Accordingly, the UE1 701 activates the f1 band, receives a referencesignal and a control signal transmitted by the small BS1 401 through thef1 band, obtains a CID of the corresponding small BS, and recognizesthat the corresponding small BS is the small BS1 401. Subsequently, theUE1 701 executes communication with the small BS1 401 according to anormal procedure.

In the same manner, the UE2 702 may recognize that a small BS that usesf3 exists a nearby region based on a signal 708 detected from the area 3713 which is stronger than a signal 707 from an area 1 711, andsubsequently, may activate the f3 band and execute communication withthe small BS2 402.

Hereinafter, the operations of a small BS and a UE associated with theabove descriptions will be described.

FIG. 8 is a diagram illustrating an operation in which a small BSgenerates and transmits an S-DS according to a first embodiment of thepresent disclosure.

In operation 801, a small BS selects at least one CC out of available NCCs. Only one CC may be selected out of the CCs selected as describedabove, by taking into consideration a traffic load of each CC,information associated with whether an adjacent small BS uses a CC, orthe like. Since this has been described in FIG. 4, detailed descriptionthereof will be omitted. In operation 803, a small BS generates an S-DSbased on the selected CC. A scheme of generating an S-DS has beendescribed with reference to FIGS. 5 and 6, and thus, a detaileddescription thereof will be omitted.

In operation 805, the generated S-DS is transmitted using an S-DCHtransmission resource of an f0 band that is determined in advance. Whenan S-DS is generated using a single code as described in FIG. 5, an S-DSfor each CC may be transmitted through a transmission resource of anS-DS corresponding to a corresponding CC. In this instance, CC-basedS-DS location information may be provided from a macro BS in advance toa small BS through a backhaul network. Also, a location of an S-DS foreach CC may be fixed to a predetermined location, or may be determinedto be different for each macro BS using a CID of a macro BS as afunction.

When an S-DS is generated using an orthogonal code having a differentvalue for each CC, as described in FIG. 6, a location where an S-DS isinserted for each CC may be identical. In this instance, the CC-basedcode information and the S-DS location information may be obtained inadvance from a macro BS through a backhaul network. Also, a CC-basedorthogonal code may be fixed to a predetermined orthogonal code, or maybe determined to be different for each macro BS using a CID of a macroBS as a function.

FIG. 9 is a diagram illustrating an operation in which a UE receives anS-DS according to various embodiments of the present disclosure.

In operation 901, a UE executes a search through a transmission resourceof an f0 band which is a CC resource of a BS, for example, apredetermined area on a PDSCH of LTE, and receives an S-DCH including anS-DS.

When an S-DS is generated using a single code as described in FIG. 5, anS-DS for each CC may be received through a transmission resource of anS-DS corresponding to a corresponding CC, in an S-DCH. In this instance,CC-based S-DS location information may be provided from a macro BS inadvance to a UE through a broadcasting message or a control message.Also, a location of an S-DS for each CC may be fixed to a predeterminedlocation, or may be determined to be different for each macro BS using aCID of a macro BS as a function.

When an S-DS is generated using an orthogonal code having a differentvalue for each CC, as described in FIG. 6, a location of an S-DCH wherean S-DS is inserted for each CC may be identical. In this instance, theCC-based code information and the S-DS location information may beobtained in advance from a macro BS through a broadcasting message or acontrol message. Also, a CC-based orthogonal code may be fixed to apredetermined orthogonal code, or may be determined to be different foreach macro BS using a CID of a macro BS as a function.

In operation 903, the strength of a signal included in the S-DCH area ismeasured and an S-DS having a reception signal strength that is greaterthan or equal to a predetermined threshold value is detected. When asmall BS generates an S-DS using an identical code value as described inFIG. 5, the UE measures the strength of a reception signal in each of NS-DS transmission areas included in the S-DCH area. Conversely, when thesmall BS generates an S-DS using an orthogonal code that has a differentvalue for one another as described in FIG. 6, the UE measures acorrelation value between a signal received in the identical S-DCH areaand each of N candidate orthogonal codes corresponding to N CCs.

In operation 905, a reception signal (that is, S-DS) that is greaterthan or equal to the predetermined threshold value is detected, and CCinformation is obtained from the detected S-DS using CC-based S-DSlocation (FIG. 5) or CC-based code information (FIG. 6).

In operation 907, a frequency band (fk) corresponding to the obtained CCinformation is activated and communication with a corresponding small BSis executed. That is, the communication with the corresponding small BSis executed by receiving a reference signal and a control signaltransmitted by the small BS in the fk band.

Second Embodiment

The second embodiment of the present disclosure is a method of operatinga small BS in a dormant mode when the small BS that does not execute thetransmission and reception of data with a UE exists, and is a method ofreporting, to a new UE, the existence of the small BS that operates inthe dormant mode when the new UE enters the coverage of the small BSthat operates in the dormant mode.

Hereinafter, a small BS that does not execute the transmission andreception of data with a UE is referred to as a “dormant mode” small BS.A small BS that executes the transmission and reception of a referencesignal, a control signal, user data, or the like, with a UE to provide anormal cellular service, is referred to as an “active mode” small BS.

In the second embodiment, when a UE to which a small BS provides aservice does not exist in the coverage of the small BS, the small BSenters a dormant mode, and suspends the transmission and reception of areference signal, a control signal, or user data. When a new UE entersthe cell coverage of the small BS that operates in the dormant mode, thesmall BS enters an active mode from the dormant mode.

FIG. 10 is a diagram illustrating a process in which a small BS isbilaterally converted between a dormant mode and an active modeaccording to a second embodiment of the present disclosure.

When it is determined that a UE does not exist in the cell coverage of asmall BS 1003 during a predetermined period of time, the small BS 1003that currently operates in an active mode enters a dormant mode inoperation 1010, and transfers, to a macro BS 1001, a dormant mode entrymessage (or indicator) indicating that the small BS 1003 enters thedormant mode, through a backhaul network in operation 1011. The macro BS1001 that receives the dormant mode entry message allocates andtransfers a dormant BS index to the small BS 1003 in operation 1013.

Here, the dormant BS index is used to distinguish small BSs that operatein a dormant mode from among a plurality of small BSs. A predeterminednumber of dormant BS indices may be set, and it is preferable that thenumber of dormant BS indices is set to be smaller than the total numberof small BSs.

For example, when it is assumed that the number of small BSs is 10, itis preferable that the number of small BSs that operate in a dormantmode out of 10 small BSs is less than 10. Therefore, when 4 out of 10small BSs operate in a dormant mode on average according to astatistical analysis, the number of dormant BS indices may be set to 4or 5 including a predetermined margin value.

In some instances, all of the 10 small BSs operate in a dormant mode. Inthis instance, when the number of UEs that operate in a dormant mode islarger than the number of dormant BS indices, a single dormant BS indexmay be allocated to a plurality of small BSs. In this instance, a macroBS allocates a single dormant BS index to small BSs that aregeographically distant from one another, so as to minimize interferencebetween S-DSs generated by the small BSs, which are assigned with theidentical dormant BS index.

Referring again to FIG. 10, the small BS 1003 that receives the dormantBS index generates an S-DS corresponding to the dormant mode index toreport the existence of the small BS 1003 in operation 1015, andtransmits the S-DS through an S-DCH of an f0 band in operation 1017. Inoperation 1019, a UE 1005 detects the S-DS. Operations 1015 to 1019 willbe described as follows.

The S-DS generated by the dormant mode small BS 1003 in operation 1015may need to be distinguished from an S-DS generated by an active modesmall BS. For reference, a method for the active mode small BS togenerate an S-DS has been described in the first embodiment.

When it is configured to generate an S-DS using a single code asdescribed in FIG. 5, an S-DCH may need to be allocated for an S-DS thatis generated by a dormant mode small BS in addition to an S-DCH for anS-DS that is generated by an active mode small BS. This will bedescribed with reference to FIG. 11.

FIG. 11 is a diagram illustrating a structure of an S-DCH according to asecond embodiment of the present disclosure.

For example, it is assumed that the total number of small BSs is set to10, the total number of CCs allocated to the small BSs is set to 5(f1˜f5), and the number of dormant BS indices is set to 4. Under theassumption, the structure of the S-DCH, according to the secondembodiment of the present disclosure, is as shown in FIG. 11.

Active mode small BSs transmit S-DSs using an S-DCH 1100 including 5resource areas 1101 to 1105 from the top, and dormant mode small BSstransmit S-DSs using an S-DCH 1110 including 4 resource areas 1111 to1114 from the bottom. In this instance, the S-DSs generated by theactive mode small BSs and S-DSs generated by the dormant mode small BSsare a single code (k) having an identical value, but have differentmeanings.

That is, the S-DSs generated by the active mode small BSs indicate afrequency band of a CC used by a corresponding small BS based on aresource area to which a corresponding S-DS is inserted. Conversely, anarea where an S-DS generated by the dormant mode small BS is determinedbased on a dormant BS index that the dormant mode small BS is assignedwith from a macro BS, and the dormant mode small BS reports that thesmall BS itself is in a dormant mode by indicating the assigned dormantBS index.

For example, when a dormant mode BS is assigned with a dormant BS index“1” from a macro BS, the corresponding dormant mode BS inserts an S-DSinto a resource area 1111 that is mapped to the dormant BS index “1”,and transmits the same. When a UE that receives the S-DS detects theS-DS from the resource area 1111, the UE may recognize that a small BSthat is assigned with the dormant BS index “1” exists in a nearbyregion.

The mapping relationship between a dormant BS index and an S-DCH, andthe S-DCH location information are agreed in advance, and may bereported to the UE through a broadcasting message, a control message, orthe like of the macro BS. Also, the information may be provided inadvance to small BSs through a backhaul network or the like. Thelocation of the S-DCH may be fixed to a predetermined area, or may bedetermined based on a function using a macro cell identification, whichhas been described above.

Generalizing the above described descriptions, when a macro BS uses atotal of K dormant BS indices, and a total of N CCs are used by smallBSs, the total number of transmission resources used to transmit S-DSsgenerated by an active mode small BS and a dormant mode BS may be N+K.

Referring again to FIG. 10, in operation 1019, the UE 1005 measures areception signal strength in resource areas in an S-DCH for a dormantmode BS, and recognizes a small BS that operates in a dormant modeexists in a nearby region when an S-DS of which a signal strength isgreater than or equal to a predetermined threshold value, is detected.

However, the UE may not know a frequency band of a CC used by thedormant mode small BS. To this end, the UE 1005 obtains a dormant BSindex from the received S-DS, and transfers the same to the macro BS1001 in operation 1021. For reference, the UE 1005 is aware of themapping relationship between detailed areas 1111 to 1114 of the S-DCH1110 for the dormant mode BS and dormant BS indices and, thus, mayrecognize an area through which the received S-DS of operation 1019 isobtained, and may obtain a dormant BS index based on the same.

The macro BS 1001 that receives the dormant BS index from the UE 1005may determine that the new UE 1005 enters the coverage of the small BS1003, and may instruct, through a backhaul network, the small BS 1003that currently operates in a dormant mode to enter an active mode inoperation 1023. Accordingly, the small BS 1003 enters an active mode inoperation 1025. Entry into an active mode indicates that the small BS1003 itself selects a CC to be used by the small BS 1003, and preparesthe execution of communication in the selected CC. A method for a smallBS to select a CC, as described in the first embodiment, may be used asa method of selecting a CC. However, depending on cases, a predeterminedCC, which is set as a default, may be used.

Subsequently, the small BS 1003 transfers the dormant BS index that wasallocated to the small BS 1003 itself, and selected CC information, tothe macro BS 1001, in operation 1027. The reason that the small BS 1003transfers the dormant BS index is to enable the dormant BS index thatwas allocated to the small BS 1003 to be allocated to another small BSthat newly enters a dormant mode, since the small BS 1003 is no longer adormant BS. That is, the small BS 1003 returns the dormant BS index.

In operation 1029, the macro BS 1001 transfers, to the UE 1005, CCinformation of the small BS 1003 through a downlink signaling of the f0band. This is to report the information associated with the CC selectedby the small BS 1003, to the UE 1005 that is aware of the existence ofthe small BS 1003, so as to enable the UE 1005 to communication with thesmall BS 1003 in a frequency band of the corresponding CC.

In operation 1031, the UE 1005 receives a reference signal and a controlsignal, and executes a cell association procedure, so as to executecommunication with the small BS 1003 in the corresponding CC frequencyband based on the CC information. In this instance, the UE 1005 may putoff the execution of the cell association procedure during apredetermined period of time until the small BS 1003 is capable ofstarting operation in an active mode, and transmitting reference signalsused for the cell association.

The descriptions of FIG. 10 have been provided by assuming that a singlecode is used when an S-DS is generated, as described in FIG. 5. When itis configured to use an orthogonal code having a different value fromone another when an S-DS is generated, as described in FIG. 6, aresource for generating an S-DS in FIG. 10 may be changed into anorthogonal code. Accordingly, an orthogonal code for an S-DS of adormant mode small BS may be used in addition to an orthogonal code foran S-DS generated by an active mode small BS. Also, the additionalorthogonal code may be mapped to a dormant BS index. Except for theabove points, the above descriptions of FIG. 10 may be applied as theyare.

That is, the small BS 1003 that is assigned with the dormant BS index“1” generates an S-DS using an orthogonal code corresponding to theindex “1”, inserts the generated S-DS into a resource area that isidentical to an S-DCH for an S-DS of the active mode small BS, andtransmits the same. As described in the first embodiment, when S-DSs aregenerated using different orthogonal codes, transmission resources,through which the S-DSs are transmitted, are identical.

In the same manner, the small BS 1003 generates an S-DS using anadditional orthogonal code for a dormant BS, and transmits the same in aresource area that is identical to an S-DCH resource area for an S-DSgenerated by the active mode small BS.

The UE 1005 may detect an S-DS from the S-DCH using an additionalcandidate orthogonal code for the dormant mode small BS, andaccordingly, may recognize that the dormant mode small BS 1003 that isassigned with the index “1” exists in a nearby region.

Third Embodiment

The first embodiment is a case in which an S-DS indicates CCinformation, and the second embodiment is a case in which an S-DSindicates a dormant BS index. According to the third embodiment, an S-DSindicates a CID configuration information index that may be used forconfiguring a CID of a small BS.

In the first embodiment, a UE detects an S-DS so as to obtain CCinformation used by an adjacent BS, and executes a search through afrequency band (fk) of the corresponding CC information so as to obtaina CID using a reference signal and a control signal transmitted by thecorresponding adjacent BS in the fk band. For example, in the existingLTE system, a CID of a small BS may be obtained using a firstsynchronization signal (PSS) and a secondary PSS of the small BS.

In the third embodiment of the present disclosure, a UE uses atransmission resource of an f0 band to enable an S-DS to indicateinformation that may configure a part of a CID. In the third embodimentof the present disclosure, information that may configure a part of theCID is referred to as “cell identification (CID) configurationinformation”, and an S-DS indicates an index of the CID configurationinformation. A method of generating and transferring an S-DS thatindicates the CID configuration information index may use a single codeor orthogonal codes having different values according to the first andthe second embodiment of the present disclosure.

That is, when a CID configuration index is configured using a singlecode as described in FIG. 5, each CID configuration information indexmay be mapped to a location of an S-DCH where an S-DS is inserted, andthereby being distinguished. Therefore, a UE obtains the CIDconfiguration information index from the DS using location informationof an S-DS for each CID configuration information index, which isprovided in advance from a macro BS.

Conversely, when a CID configuration information index is configuredusing an orthogonal code having a different value for one another, eachCID configuration information index may be mapped by a differentorthogonal code, and may be thereby distinguished. Therefore, a UEobtains the CID configuration information index using the mappingrelationship between CID configuration information indices andorthogonal codes, and S-DS location information, which are provided inadvance from a macro BS.

According to the third embodiment of the present disclosure, when it isassumed that a total of L CID configuration information indices areused, the number of CIDs may be increased to be L times greater than thenumber of CIDs used in the existing LTE system. Table 1 as providedbelow shows that (504 X L) CIDs may be generated by combining CIDconfiguration information indices and the existing PSSs and SSSs, when Lpieces of CID configuration information are assumed. That is, in theexisting LTE system, a total of 504 CID indices (D) may be generatedusing a PSS index (A) and an SSS index (C). According to the thirdembodiment of the present disclosure, a CID configuration informationindex (A) is additionally used, and thus, a total of 504 X L CID indicesmay be generated.

TABLE 1 CID configuration information index (A) PSS index (B) SSS index(C) CID index (D) 1 1 1, 2, . . . , 167, 168 1, 2, . . . , 167, 168 2 1,2, . . . , 167, 168 169, 170, . . . , 335, 336 3 1, 2, . . . , 167, 168337, 338, . . . , 503, 504 2 1 1, 2, . . . , 167, 168 505, 506, . . . ,671, 672 2 1, 2, . . . , 167, 168 673, 674, . . . , 839, 840 3 1, 2, . .. , 167, 168 841, 842, . . . , 1007, 1008 . . . . . . . . . . . . L 1 1,2, . . . , 167, 168 504(L − 1) + 1, . . . , 504(L − 1) + 168 2 1, 2, . .. , 167, 168 504(L − 1) + 169, . . . , 504(L − 1) + 336 3 1, 2, . . . ,167, 168 504(L − 1) + 337, . . . , 504L

Hereinafter, configurations of a small BS and a UE according toembodiments of the present disclosure will be described.

FIG. 12 is a diagram illustrating a configuration of another small BSaccording to various embodiments of the present disclosure.

From the perspective of the first embodiment, the operations of a smallBS 1200 will be described first.

The small BS 1200 includes a transceiving unit 1201, a controller 1203,and an S-DS generating unit 1205.

The transceiving unit 1201 includes an RF unit to execute thetransmission and reception of a signal with a macro BS and a UE, in anf0 band.

The controller 1203 selects at least one CC out of N available CCs, andtransmits the same to the S-DS generating unit 1205. As described inFIG. 4, only one CC may be selected out of the selected CCs by takinginto consideration a traffic load of each CC, information associatedwith whether an adjacent small BS uses a CC, or the like.

Also, the controller 1203 may receive CC-based S-DS location information(FIG. 5) or CC-based code information and S-DS location information(FIG. 6), in advance from a macro BS through a backhaul network, andtransfer the same to the S-DS generating unit 1205.

When an S-DS is generated using a single code as described in FIG. 5, anS-DS for each CC may be transmitted through a transmission resource ofan S-DS corresponding to a corresponding CC. In this instance, CC-basedS-DS location information may be provided from the macro BS in advanceto the controller 1203 through a backhaul network. Also, a location ofan S-DS for each CC may be fixed to a predetermined location, or may bedetermined to be different for each macro BS using a CID of a macro BSas a function. When an S-DS is generated using an orthogonal code havinga different value for each CC, as described in FIG. 6, a location wherean S-DS is inserted for each CC may be identical. In this instance, thecontroller 1203 may obtain the CC-based code information and the S-DSlocation information in advance from the macro BS through the backhaulnetwork. Also, a CC-based orthogonal code may be fixed to apredetermined orthogonal code, or may be determined to be different foreach macro BS using a CID of a macro BS as a function.

The S-DS generating unit 1205 generates an S-DS corresponding to the CCselected by the controller 1203, and transmits the generated S-DS usingan S-DCH transmission resource of the f0 band, based on the CC-basedS-DS location information (FIG. 5) or CC-based code information and S-DSlocation information (FIG. 6), which is transferred from the controller1203.

From the perspective of the second embodiment, the operations of thesmall BS 1200 will be described.

In the second embodiment, when the controller 1203 determines that a UEdoes not exist in the cell coverage of the small BS 1200 during apredetermined period of time, the small BS 1200 enters a dormant mode,and the controller 1203 generates a dormant mode entry messageindicating that the small BS 1200 enters the dormant mode and reportsthe same to a macro BS through the transceiving unit 1201.

Subsequently, when a dormant BS index is received from the macro BS, thecontroller 1203 transfers the dormant BS index to the S-DS generatingunit 1205 and instructs the generation of information that indicates adormant mode small BS. The S-DS generating unit 1205 generates an S-DSfor reporting that the small BS 1200 is a dormant small BS, andtransmits the same through the transceiving unit 1201. Except for theabove, a scheme of generating an S-DS and a transmitted resource areidentical to the descriptions in the first embodiment, and thus, thedescriptions thereof will be omitted.

From the perspective of the third embodiment, the operations of thesmall BS 1200 will be described.

In the third embodiment, the controller 1203 transfers a CIDconfiguration information index associated with a CID of the small BS1200 using an S-DS, and transfers, to the S-DS generating unit 1205,S-DS location information for each CID configuration information index(FIG. 5) or orthogonal code information for each CID configurationinformation index and S-DS location information (FIG. 6), and the S-DSgenerating unit 1205 generates an S-DS under the control of thecontroller 1203 and transmits the same through the transceiving unit1201. Other configurations are identical to the first embodiment.

FIG. 13 is a diagram illustrating a UE according to various embodimentsof the present disclosure.

From the perspective of the first embodiment, the operations of a UE1300 will be described.

A transceiving unit 1301 executes a search through a transmissionresource of an f0 band which is a CC resource of a macro BS, forexample, a predetermined area on a PDSCH of LTE, and receives an S-DCHincluding an S-DS.

When an S-DS is generated using a single code as described in FIG. 5, anS-DS for each CC may be received through a transmission resource of anS-DS corresponding to a corresponding CC, in an S-DCH. In this instance,CC-based S-DS location information may be provided from a macro BS inadvance to a UE through a broadcasting message or a control message.Also, the location of an S-DS for each CC may be fixed to apredetermined location, or may be determined to be different for eachmacro BS using a CID of a macro BS as a function. When an S-DS isgenerated using an orthogonal code having a different value for each CC,as described in FIG. 6, a location of an S-DCH where an S-DS is insertedfor each CC may be identical. In this instance, the CC-based codeinformation and the location information of an S-DS may be obtained inadvance from a macro BS through a broadcasting message or a controlmessage. Also, a CC-based orthogonal code may be fixed to apredetermined orthogonal code, or may be determined to be different foreach macro BS using a CID of a macro BS as a function.

An S-DS detecting unit 1303 measures the strength of a signal includedin the S-DCH area, and detects an S-DS having a reception signalstrength that is greater than or equal to a predetermined thresholdvalue. When a small BS generates an S-DS using a single code asdescribed in FIG. 5, the S-DS detecting unit measures the strength of areception signal in each of N S-DS transmission areas included in theS-DCH area. Conversely, when the small BS generates an S-DS using anorthogonal code having a different value from one another, as describedin FIG. 6, the S-DS detecting unit 1303 measures a correlation valuebetween a signal received in the identical S-DCH area and each of Ncandidate orthogonal codes corresponding to N CCs. Subsequently, theS-DS detecting unit 1303 detects a reception signal (that is, S-DS) thatis greater than or equal to a threshold value.

A controller 1305 obtains CC information using CC-based S-DS locationinformation (FIG. 5) or CC-based code information (FIG. 6) thatcorresponds to the detected S-DS. A frequency band (fk) corresponding tothe obtained CC information is activated and communication with acorresponding small BS is executed. That is, the communication with thecorresponding small BS is executed by receiving a reference signal and acontrol signal transmitted by the small BS in the fk band.

From the perspective of the second embodiment, the operations of the UE1300 will be described.

The S-DS detecting unit 1303 measures the reception signal strength inthe resource areas of an S-DCH for a dormant mode BS, and detects anS-DS of which the signal strength is greater than or equal to apredetermined threshold value.

The controller 1305 obtains a dormant BS index from the detected S-DS,and transfers the same to a macro BS. For reference, the controller 1305receives the mapping relationship between detailed areas of the S-DCHfor a dormant mode BS and dormant BS indices, in advance from the macroBS, and may recognize an area where the received S-DS is obtained andmay obtain the dormant BS index based on the same.

Also, the controller 1305 receives CC information used by the dormantmode small BS, from the macro BS, activates the corresponding CCfrequency band (fk) based on the corresponding CC information, receivesa reference signal and a control signal from the small BS, and executesa cell association procedure. Other configurations are identical to thefirst embodiment.

From the perspective of the third embodiment, the operations of the UE1300 will be described.

In the third embodiment, the transceiving unit 1301 executes a searchthrough a transmission resource of an f0 band, which is a CC resource ofthe macro BS, for example, a predetermined area on a PDSCH of LTE, andreceives an S-DCH including an S-DS.

When an S-DS is generated using a single code as described in FIG. 5, anS-DS for each CID configuration information index may be receivedthrough a transmission resource of an S-DS corresponding to acorresponding CID configuration information index, in an S-DCH. In thisinstance, S-DS location information for each CID configurationinformation index may be provided from the macro BS in advance to thecontroller 1305 through a broadcasting message or a control message.Also, S-DS location information for each CID configuration informationindex may be fixed to a predetermined location, or may be determined tobe different for each macro BS using a CID of a macro BS as a function.When an S-DS is generated using an orthogonal code having a differentvalue from one another, as described in FIG. 6, a location of an S-DCHwhere an S-DS is inserted for each CID configuration information indexmay be identical.

In this instance, the orthogonal code information for each CIDconfiguration information index and the S-DS location information may beobtained in advance from the macro BS through a broadcasting message ora control message. Also, an orthogonal code for each CID configurationinformation index may be fixed to a predetermined orthogonal code, ormay be determined to be different for each macro BS using a CID of amacro BS as a function.

The S-DS detecting unit 1303 measures the strength of a signal includedin the S-DCH area, and detects an S-DS having a reception signalstrength that is greater than or equal to a predetermined thresholdvalue. When an S-DS is generated using a single code as described inFIG. 5, the S-DS detecting unit 1303 measures the strength of areception signal in each of L S-DS transmission areas included in theS-DCH area.

Conversely, when an S-DS is generated using an orthogonal code that hasa different value from one another, as described in FIG. 6, the S-DSdetecting unit 1303 measures a correlation value between a signalreceived in the identical S-DCH area and each of L candidate orthogonalcodes corresponding to L CID configuration information indices.Subsequently, the S-DS detecting unit 1303 detects a reception signal(that is, S-DS) that is greater than or equal to a threshold value.

The controller 1305 obtains a CID configuration information index fromthe detected S-DS, using S-DS location information for each CIDconfiguration information index (FIG. 5) or orthogonal code informationfor each CID configuration information index and S-DS locationinformation (FIG. 6). Also, the obtained CID configuration informationindex may be used when a CID is generated. That is, a PSS and an SSS arereceived through the communication with a small BS, and a CID of thecorresponding small BS is generated.

Hereinafter, the operations of a macro BS, according to the secondembodiment of the present disclosure, will be described.

In operation 1401, the macro BS receives a dormant mode entry messagefrom a small BS. In operation 1403, the macro BS transmits a dormant BSindex to the small BS. In a state in which a predetermined number ofdormant BS indices are set, a subsequent dormant BS index is transmittedfor a subsequent small BS that enters a dormant mode. The dormant BSindex may be generated before or after the reception of the dormant modeentry message.

In operation 1405, the macro BS receives a dormant BS index from a UE.This is a dormant BS index that the UE obtains from an S-DS that a smallBS generates and transmits. When the macro BS receives the dormant BSindex from the UE, the macro BS recognizes that a new UE enters thecoverage of the small BS. Accordingly, the macro BS generates andtransfers an active mode entry message to the small BS so as to instructthe small BS to enter an active mode in operation 1407. Subsequently, inoperation 1409, the macro BS receives, from the small BS that enters theactive mode, the dormant BS index and CC information used by thecorresponding small BS. In operation 1411, the macro BS transmits thereceived CC information to the UE, so as to enable the UE to executecommunication with the small BS in the corresponding CC frequency band.

FIG. 15 is a diagram illustrating a macro BS 1500 according to a secondembodiment of the present disclosure.

A transceiving unit 1501 receives a dormant mode entry message from asmall BS, and transfers the same to a controller 1503.

The controller 1503 instructs a message generating unit 1505 to generatea dormant BS index so as to instruct the small BS to enter a dormantmode.

The message generating unit 1505 generates a dormant BS index to beallocated to a small BS according to a sequence of an index, andtransmits the same through the transceiving unit 1501. When thecontroller 1503 receives the dormant BS index from the UE through thetransceiving unit 1501, the controller 1503 determines that a new UEenters the coverage of the small BS and instructs the message generatingunit 1505 to generate an active mode entry message. The messagegenerating unit 1505 generates the active mode entry message under thecontrol of the controller 1503, and transfers the same to the small BSthrough the transceiving unit 1501.

Subsequently, when the controller 1503 receives a dormant BS index andCC information used by a corresponding small BS from the small BS thatenters the active mode, the controller 1503 reserves the dormant BSindex for a subsequent dormant BS, and transmits the received CCinformation to the UE so as to enable the UE to execute communicationwith the small BS in the corresponding CC frequency band.

The embodiments of the present disclosure have been described in detail.According to the present disclosure, a discovery signal generated by asmall BS is transmitted using a transmission resource of a macro BS. Inthis instance, information used for the communication between the smallBS and a UE may be included in the discovery signal. Through the above,a UE may not waste power to execute a search through a frequency band ofthe small BS, and the UE promptly obtains information associated withthe small BS, and thus, a delay time caused by searching for the smallBS may be reduced.

While the present disclosure has been shown and described with referenceto various embodiments thereof, it will be understood by those skilledin the art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the present disclosure asdefined by the appended claims and their equivalents.

1. A method for a second base station (BS) to transmit a discoverysignal (DS) in a mobile communication system that includes a first BS,to which a component carrier (CC) of a predetermined frequency band isassigned, and at least one second BS to which N CCs are assigned, ofwhich a frequency band is different from the CC assigned to the firstBS, the method comprising: generating a DS corresponding topredetermined information; and transmitting the generated DS through adiscovery channel (DCH) that is formed of transmission resources of thefirst BS, wherein the predetermined information is one of at least oneCC information used by the second BS, a cell ID (CID) configurationinformation index of the second BS, and a dormant BS index when thesecond BS is in a dormant mode.
 2. The method as claimed in claim 1,wherein the generating of the DS comprises: generating the DS using asingle predetermined code or a predetermined number of orthogonal codeshaving different values.
 3. The method of claim 2, wherein, when thepredetermined information is the CC information and the DS is generatedusing a single predetermined code, the DCH includes N transmission areasthat are mapped respectively to N CC values, and wherein the DS istransmitted through a transmission area that is mapped to a CCinformation value corresponding to the DS.
 4. The method of claim 2,wherein, when the predetermined information is the CC information andthe DS is generated using a predetermined number of orthogonal codes,the orthogonal codes are formed of N orthogonal codes that are mappedrespectively to N CC information values, and wherein the DCH includes asingle transmission area for the transmission of the DS, and the DS istransmitted through the single transmission area for the transmission ofthe DS, irrespective of the CC information value.
 5. The method of claim2, wherein, when the predetermined information is a CID configurationinformation index of the second BS, and the DS is generated using asingle predetermined code, the DCH includes L transmission areas thatare mapped respectively to L CID configuration information index values,and wherein the DS is transmitted through a transmission area that ismapped to a CID configuration information index value corresponding tothe DS.
 6. The method of claim 2, wherein, when the predeterminedinformation is a CID configuration information index of the second BS,and the DS is generated using a predetermined number of orthogonalcodes, the orthogonal codes are formed of L orthogonal codes that aremapped respectively to L CID configuration information index values,wherein the DCH includes a single transmission area for the transmissionof the DS, and wherein the DS is transmitted through the singletransmission area for the transmission of the DS, irrespective of theCID configuration information index value.
 7. The method of claim 1,wherein the DCH area is determined based on DCH location informationthat is transferred in advance from the first BS, and wherein the DCHlocation information is fixed to a predetermined area from amongtransmission resources of the first BS or is determined based on a CIDof the first BS.
 8. A method for a user equipment (UE) to receive adiscovery signal (DS) of a second base station (BS), in a mobilecommunication system that includes a first BS to which a componentcarrier (CC) of a predetermined frequency band is assigned, and at leastone second BS to which N CCs are assigned, of which a frequency band isdifferent from the CC assigned to the first BS, the method comprising:receiving a discovery channel (DCH) formed of transmission resourcesallocated to the first BS; detecting a DS indicating predeterminedinformation from the received DCH; and obtaining predeterminedinformation from the detected DS, wherein the predetermined informationis one of at least one CC information used by the second BS, cell ID(CID) index information of the second BS, and a dormant BS index whenthe second BS is a dormant mode.
 9. The method of claim 8, wherein thedetecting of the DS comprises: detecting the DS using a singlepredetermined code or a predetermined number of orthogonal codes havingdifferent values.
 10. The method of claim 9, wherein, when thepredetermined information is the CC information and the DS is detectedusing a single predetermined code, the DCH includes N transmission areasthat are mapped respectively to N CC values, and wherein the DS isdetected through a transmission area that is mapped to a CC informationvalue indicated by the DS.
 11. The method of claim 9, wherein, when thepredetermined information is the CC information and the DS is detectedusing a predetermined number of orthogonal codes, the orthogonal codesare formed of N orthogonal codes that are mapped respectively to N CCinformation values, and wherein the DCH includes a single transmissionarea for the transmission of the DS, and the DS is detected through thesingle transmission area for the transmission of the DS, irrespective ofthe CC information value.
 12. The method of claim 9, wherein, when thepredetermined information is a CID configuration information index ofthe second BS and the DS is generated using a single predetermined code,the DCH includes L transmission areas that are mapped respectively to LCID configuration information index values, and wherein the DS isdetected through a transmission area that is mapped to a CIDconfiguration information index value indicated by the DS.
 13. Themethod of claim 9, wherein, when the predetermined information is a CIDconfiguration information index of the second BS and the DS is detectedusing a predetermined number of orthogonal codes, the orthogonal codesare formed of L orthogonal codes that are mapped respectively to L CIDconfiguration information index values, wherein the DCH includes asingle transmission area for the transmission of the DS, and wherein theDS is detected through the single transmission area for the transmissionof the DS, irrespective of the CID configuration information indexvalue.
 14. The method of claim 8, wherein the DCH area is determinedbased on DCH location information that is transferred in advance fromthe first BS, and wherein the DCH location information is fixed to apredetermined area from among transmission resources of the first BS, oris determined by a CID of the first BS.
 15. An apparatus of a secondbase station (BS) for transmitting a discovery signal (DS), in a mobilecommunication system that includes a first BS to which a componentcarrier (CC) of a predetermined frequency band is assigned, and at leastone second BS to which N CCs are assigned, of which a frequency band isdifferent from the CC assigned to the first BS, the apparatuscomprising: a controller configured to transfer predeterminedinformation to a DS generating unit, the DS generating unit beingconfigured to generate a DS corresponding to the predeterminedinformation; and a transceiving unit configured to transmit thegenerated DS through a discovery channel (DCH) that is formed oftransmission resources of the first BS, wherein the predeterminedinformation includes one of at least one CC information used by thesecond BS, CID index information of the second BS, and a dormant BSindex when the second BS is in a dormant mode.
 16. The apparatus ofclaim 15, wherein the DS generating unit generates the DS using a singlepredetermined code or a predetermined number of orthogonal codes havingdifferent values.
 17. The apparatus of claim 16, wherein, when thepredetermined information is the CC information and the DS is generatedusing a single predetermined code, the DCH includes N transmission areasthat are mapped respectively to N CC values, and wherein the DS istransmitted through a transmission area that is mapped to a CCinformation value corresponding to the DS.
 18. The apparatus of claim16, wherein, when the predetermined information is the CC informationand the DS is generated using a predetermined number of orthogonalcodes, the orthogonal codes are formed of N orthogonal codes that aremapped respectively to N CC information values, wherein the DCH includesa single transmission area for the transmission of the DS, and whereinthe DS is transmitted through the single transmission area for thetransmission of the DS, irrespective of the CC information value. 19.The apparatus of claim 16, wherein, when the predetermined informationis a CID configuration information index of the second BS and the DS isgenerated using a single predetermined code, the DCH includes Ltransmission areas that are mapped respectively to L CID configurationinformation index values, and wherein the DS is transmitted through atransmission area that is mapped to a CID configuration informationindex value corresponding to the DS.
 20. The apparatus of claim 16,wherein, when the predetermined information is a CID configurationinformation index of the second BS, and the DS is generated using apredetermined number of orthogonal codes, the orthogonal codes areformed of L orthogonal codes that are mapped respectively to L CIDconfiguration information index values, wherein the DCH includes asingle transmission area for the transmission of the DS, and wherein theDS is transmitted through the single transmission area for thetransmission of the DS, irrespective of the CID configurationinformation index value.
 21. The apparatus of claim 15, wherein the DCHarea is determined by DCH location information that is transferred inadvance from the first BS, and wherein the DCH location information isfixed to a predetermined area from among transmission resources of thefirst BS or is determined by a CID of the first BS.
 22. An apparatus ofa user equipment (UE) for receiving a discovery signal (DS) a secondbase station (BS), in a mobile communication system that includes afirst BS to which a component carrier (CC) of a predetermined frequencyband is assigned, and at least one second BS to which N CCs areassigned, of which a frequency band is different from the CC assigned tothe first BS, the apparatus comprising: a transceiving unit configuredto receive a discovery channel (DCH) that is formed of transmissionresources allocated to the first BS; a DS detecting unit configured todetect a DS indicating predetermined information from the received DCH;and a controller configured to obtain the predetermined information fromthe detected DS, wherein the predetermined information includes one ofat least one CC information used by the second BS, CID index informationof the second BS, and a dormant BS index when the second BS is in adormant mode.
 23. The apparatus of claim 22, wherein the DS detectordetects the DS using a single predetermined code and a predeterminednumber of orthogonal codes having different values.
 24. The apparatus ofclaim 23, wherein, when the predetermined information is CC informationand the DS is detected using a single predetermined code, the DCHincludes N transmission areas that are mapped respectively to N CCvalues, and wherein the DS is detected through a transmission area thatis mapped to a CC information value indicated by the DS.
 25. Theapparatus of claim 23, wherein, when the predetermined information isthe CC information and the DS is detected using a predetermined numberof orthogonal codes, the orthogonal codes are formed of N orthogonalcodes that are mapped respectively to N CC information values, whereinthe DCH includes a single transmission area for the transmission of theDS, and wherein the DS is detected through the single transmission areafor the transmission of the DS irrespective of the CC information value.26. The apparatus of claim 23, wherein, when the predeterminedinformation is a CID configuration information index of the second BSand the DS is generated using a single predetermined code, the DCHincludes L transmission areas that are mapped respectively to L CIDconfiguration information index values, and wherein the DS is detectedthrough a transmission area that is mapped to a CID configurationinformation index value indicated by the DS.
 27. The apparatus of claim23, wherein, when the predetermined information is a CID configurationinformation index of the second BS and the DS is detected using apredetermined number of orthogonal codes, the orthogonal codes areformed of L orthogonal codes that are mapped respectively to L CIDconfiguration information index values, wherein the DCH includes asingle transmission area for the transmission of the DS, and wherein theDS is detected through the single transmission area for the transmissionof the DS irrespective of the CID configuration information index value.28. The apparatus of claim 22, wherein the DCH area is determined basedon DCH location information that is transferred in advance from thefirst BS, and wherein the DCH location information is fixed to apredetermined area from among transmission resources of the first BS oris determined by a CID of the first BS.